This invention relates generally to systems and processes for mounting and very accurately positioning rotating rolls acting in cooperation with an opposed anvil roll on a material or web passing through the roll nip. More specifically, it relates to a roll mounting and positioning system for inline web finishing equipment for use in conjunction with a web printing press.
Rotary die cutters are well known for cutting apertures of various sizes and shapes in a running web, particularly a web operating in conjunction with a printing press. A classic application of such die cutters is to cut out a set of peel-off labels carried on a backing sheet. Reduced to its essentials, known rotary die cutters utilize a pair of rolls rotating about two parallel axes that are rotatably mounted between a pair of side frames and driven by a line shaft which also powers the printing press. One roll, designated as the die roll, or cylinder, carries flexible sheet metal dies on its outer surface which are the cutting members. Each die is formed from a thin metal sheet and has raised cutting edges formed in the shape of an aperture to be cut. The die is wrapped around the die cylinder and replaceably secured to it, usually utilizing magnetic attraction produced by embedded permanent magnets in the die cylinder. Dies can also be secured by tapes, mechanical clamps, or other types of fasteners. The anvil cylinder is formed of a hardened material and is of such diameter that its surface speed is substantially equal to web speed.
As the web passes between the rotating cylinders, the cutting edges of the die are pressed into the web backed up by the anvil cylinder to produce the desired aperture in the web. To the best of applicant's knowledge, heretofore such rotary die cutters, at least when used in printing press applications, have always end-mounted both the die roll and the anvil roll and side frames. Because the web leaving the printing press has a substantial width, a significant problem has been the deflection of the die roll caused by operating forces, machine distortions, vibrations, and thermal expansions. The traditional solution has been to utilize a roll having a sufficiently large diameter that it is able to resist any significant deflection. This works, but the necessary roll diameter has been such that for most product lengths (cut offs) there is a "double repeat", that is, the image or pattern being printed is repeated during one revolution of the die cylinder.
The disadvantage of this solution is that a die cylinder with a double repeat diameter is massive and costly to manufacture, particularly where the outer surface of the die cylinder must be machined to extremely tight tolerances. In addition, the substantial rotational inertia of such a large diameter die roll is an impediment to achieving a fast stop of the printing line during an emergency stop.
Other disadvantages relate to the need to have the apertures extremely accurately located so that they are in registration with the pattern printed on the web. A "vertical" adjustment of the die, one affecting the spacing between the die and anvil rolls, is also important to adjust the spacing between the cutting edges of the die and the anvil cylinder. This is important, for example, so that the die achieves a reliable cut in the web, the cutting edge does not strike the anvil cylinder and become dulled or damaged, and so that the correct spacing occurs across the full length of the die roll. In addition, as is well known to those skilled in the art, even when proper adjustments in the position of the dies are made, changes in factors such as the web material, wear of the die, and shifts in the relative position of components due to thermal expansion can require periodic readjustments of the die positions in order to have reliable apertures continue to be cut in the web.
In the prior art systems, the principal technique currently used to adjust the vertical position of a die with respect to a die roll is to place a shim between the die and the roll manually. This is a tedious and time-consuming procedure since the shims must be positioned with the die cutter stopped, the selection and placement of the shim is to some extent guesswork, and then the adjustment must be measured or tested by operating the die cutter to observe the effect of the adjustment. Not only does this procedure suffer from the fact that it is manual and requires at least a modest degree of skill, but also it requires that the printing press be stopped while the adjustments are made and checked. As is well known, any stoppage of the press is costly in terms of lost productivity. In addition, in placing the shim there is always a risk that the correct axial or circumferential positioning of the die in the roll may be lost requiring still further adjustments. It is also very important to note that the positioning must be controlled to extremely tight tolerances. Typically, control to one-tenth of a mil ( 0.0001 inch) is required.
Another known technique for changing the axis to axis (vertical) spacing of the rolls is to mount at least one of the rolls on an eccentric so that its center line location can be varied between two extreme positions. Such adjustments cannot be made on the run, that is, while the press is running and the web is passing through the rotating die cutter cylinders. Axial and circumferential adjustments of the die also require that the press be stopped while the die position is manually shifted on the die cylinder and reset. The adjustment process is manual, time-consuming, and cannot be made on the run. Also, eccentric adjustments do not provide the fine degree of adjustment often required to compensate for wear or the other factors listed above. When eccentrics have been used while the rotary die cutter is operating, they have been used most often to move the die roll a substantial distance to go "off impression", that is, moving the die cylinder away from the web to allow operation of the press line without operation of the die cutter.
It is also significant to note that conventional rotary die cutters utilize only one die cylinder and that the only practical way to adjust the axial or side to side position of the web is to shift the lateral position of the web as it passes through the cutter. This web shift works, but it has a significant disadvantage in that it requires that all of the other pieces of equipment in the line, such as gluers, perforators, numbering machines or plow stations, also be adjusted with respect to the web to maintain registration. This multiple adjustment of a series of machines to the web shift is time-consuming and tedious. However, no rotary die cutters presently known to applicants are capable of an axial or "sidelay" adjustment of the cutter.
It is therefore a principal object of this invention to provide a mounting and positioning system for a rotary die cutter which utilizes a small diameter, single repeat roll and yet which exhibits extreme rigidity.
Another principal object of the invention is to provide a mounting and positioning system with the foregoing advantages which provides extremely accurate positioning of the die with respect to the web and its anvil roll, vertically, axially, and circumferentially.
Yet another principal object of the invention is to provide a rotary die cutter positioning and mounting system with the foregoing advantages where the foregoing adjustments can be made with extreme accuracy, independently of one another, and while the die cutter is operating.
A further object of the invention is to provide a rotary die cutter mounting and positioning system which can be set up or adjusted within extremely short make ready time as compared to conventional systems currently in use.
Still another object of the invention is to provide a mounting and positioning system for a rotary die cutter which can mount two or more die rolls in an axially spaced relationship operating in cooperation with the same anvil where each die roll can be adjusted vertically and axially independently of the other with all of the foregoing advantages.
Another object of the invention is to provide a roll positioning and mounting system for a rotary die cutter for use in connection with a printing press which can handle a full width web offset, or can simultaneously run jobs having different dies or die patterns side-by-side.
A further object of the invention is to provide a mounting and positioning system for a rotary die cutter which has a reduced rotational inertia as compared to prior art devices and therefore can be brought to an emergency stop more quickly.
Still another object is to provide a mounting and positioning system for a rotary die cutter which has a favorable cost of manufacture and which requires fewer dies for operation since the pattern can be completed once every revolution rather than twice as was the case with prior art devices.
Yet another advantage is to provide a mounting and positioning system with the foregoing advantages which also provides a rapid off-impression capability.